Epoxy-functional polyurethanes and high solids thermosetting coating compositions thereof

ABSTRACT

Disclosed herein is a low molecular weight epoxy-functional polyurethane and high solids thermosetting coating compositions prepared therewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to thermosetting coating compositions andmethods of making and using the same. More specifically, the presentinvention relates to epoxy-functional polyurethane resins which areuseful in making coatings which can be hard and/or flexible and have aremarkable appearance.

2. Brief Description of the Prior Art

Recent advances in coating technology have provided coatings which aresuitable for use over various substrates which are difficult to coat.Coatings of excellent appearance, a high order of durability and havingthe ability to withstand severe environmental conditions have beenobtained. Among the more advanced coatings are those employed onvehicles, such as automobiles, where good appearance must be maintainedover long periods despite exposure to weather and various forms ofattack during use.

For some time now elastomeric material which are rubbery, and resilientmaterials have been used for areas which are subject to mechanical shocksuch as automobile bumpers and moldings, exposed corners and surfaces ofindustrial machines, kickplates and other areas of doors and entrances,and the like. The use of such elastomeric materials aids in providingprotection against permanent structural damage, but in order to attainthe desired appearance a decorative and protective coating must beapplied to the surface. Conventional coatings, including those employedon rubber and similar extensible objects must have the requiredcombination of properties. These necessary properties include:Extensibility--This property is necessary in order that the advantagesof the resilient substrate can be utilized without destruction of theintegrity of the surface of the coating. Tensile Strength--A high degreeof tensile strength is also necessary in order to avoid rupture of thefilm during use. Film Stability--Certain coatings which are extensibleand which have a relatively high tensile strength lose these propertiesupon aging and particularly if the coating is exposed to sunlight,weathering, etc. Impact resistance--The coating should have adequateimpact resistance at various temperatures as encountered in extremeweather variations. Adhesion--The coating should have satisfactoryadhesion to the various substrates with which it is to be employedincluding extensible materials such as foams, rubber and the like, andmetals such as mild steel. In addition the coatings should havesatisfactory intercoat adhesion with succeeding coats or with variousprimers which can be employed. Chemical and Humidity Resistance--Thisincludes properties such as saponification resistance upon exposure toacids and alkalis, resistance to various solvents and resistance toatmosphere of high humidity and heat.

Still other properties which are important for commercial applicabilityinclude hardness and mar resistance which make the coating particularlysuitable for hard metallic substrates. Ideally, if a coating has thehardness suitable for metal substrates and is at the same time flexible,one can use the same coating for metallic and elastomeric substrates.Such a coating is described as a universal coating.

Yet other properties which are important for commercial applicabilityinclude sprayability at high solids and low volatile organic content.

It is especially difficult to obtain the above properties in combinationsince, in most instance, the obtention of one or several of theproperties desired requires the use of materials and formulations whichunder ordinary circumstances tend to make the other desired propertiesless satisfactory. The present invention provides coating compositionsthat can have desirable combinations of properties disclosed herein.

SUMMARY OF THE INVENTION

In accordance with the foregoing, the present invention encompasses alow molecular weight epoxy-functional polyurethane resin comprising:

(a) an isocyanate, and

(b) a hydroxyl-functional polyepoxide having 2 or more epoxy group permolecule.

The invention further encompasses high solids thermosetting coatingcompositions comprising the above epoxy-functional polyurethane and acuring agent selected from the group consisting of a polyacid, ananhydride, a polyamine and mixture thereof. The coating compositions ofthis invention are characterized by high sprayability, acceptable sagcontrol, low volatile organic content, a remarkable appearance,hardness, flexibility and other desirable film properties. Hence, thecoatings can be used as elastomeric or universal coatings.

By the term "elastomeric coating" is meant that the coating is flexibleand hard enough to be useful particularly as a topcoat on elastomericsubstrates. By the term "universal coating" is meant that the coating isconjointly flexible and relatively harder than that which is requiredfor elastomeric substrates, thus, making said coating usefulparticularly as a topcoat on elastomeric and (hard) metallic substrates.

In this text, the terms molecular weight, thermosetting, solids content,sprayability, volatile organic content (VOC), flexibility, hardness andappearance are defined as follows. The term "molecular weight" refers toa number average molecular weight as determined by gel permeationchromatography using a (polystyrene or glycol) standard. Therefore, itis not the actual molecular weight which is measured but a numberaverage molecular weight which is relative to the (glycol orpolystyrene) standard.

In this context, by the term "thermosetting" is meant that the coatingcomposition, upon heating, changes irreversibly from a fusible andsoluble material into one which is infusible and insoluble through theformation of covalently crosslinked thermally stable network.

The solids content of a composition is determined by ASTM D-2369 testingmodified as follows: 0.3 grams of the composition is mixed with 5milliliters of 1:1 mixture of acetone and tetrahydrofuran and heatedtypically at 110° C. for 1 hour in a forced draft oven. The compositionis then cooled in a desiccator, reweighed and the nonvolatile contentcalculated. The percentage by weight of the composition remaining is thesolids content.

The term "sprayability" means the maximum concentration of solids atwhich the coating composition can form a uniformly deposited coating,under normal spraying conditions of, say, temperature, pressure, andspray equipment design such as entails the use of an air suction gunoperating at 60 psi with a No. 30 air cap. This maximum concentration issolvent dependent and usually occurs in a viscosity range of 20 to 80and preferably at about 22 to 24 seconds with a No. 4 Ford cup at roomtemperature after thinning with a solvent such as a mixture of methylamyl ketone and ethoxyethyl acetate or the like. Above this maximumconcentration, appearance as manifested by leveling and solvent poppingbecomes unacceptable.

The VOC is defined as the weight per volume of any compound of carbonwhich evaporates from a paint or related coating material under thespecific conditions for the determination of the non-volatile content ofthat material. Thus, the water content of the material undergoinganalysis must be determined. To obtain the VOC of a sample, thenon-volatile content, water content and the density of the material aredetermined. The VOC number is calculated by correcting the total organicvolatile content for the water content and dividing by the volume of thepaint corrected for the water content. The determination of the VOC isby ASTM D-3960 testing which entails heating the paint or relatedcoating material at 110° C. for 1 hour.

The flexibility property of the coating can be determined by spraycoating an elastomeric substrate and curing the coating at optimumconditions to give a dry film thickness of 1.5 to 2 mils. Theelastomeric substrate is 1/16 to 3/16, typically 1/8-inch thick,thermoplastic polyurethane, such as commercially available from MobayCompany as TEXIN 355D. The coated substrate is bent around a 1/2-inchdiameter mandrel with the coating side facing outward. After bending,the coating is examined for breaks and cracks. Testing can be conductedat standard temperatures such as room temperature, that is, 72°-77° F.,or at lower temperatures. The lower temperatures can be obtained bycooling the substrate to standard temperatures of 45° F., 35° F., or 0°F. before bending. The lower the temperature, the more stringent thetest. Preferably, the coating can withstand bending at 20° F., morepreferably 0° F. The flexibility property of the coating is consideredas good when there is no break in the coating or substantially no break,i.e., when the occurring break is not completely across the width of thesubstrate which is about 1 to 3 inches, at the measured temperature.Usually for elastomeric coatings, flexibility at 0° F. or lower isdesirable.

The hardness property of the coating composition can be determined bythe Sward method using a Sward Rocker as described in ORGANIC COATINGTECHNOLOGY, Payne, Vol. 1, 1965, pages 642-643. Testing is done on anoptimally cured coating having a dry film thickness of 11/4 to 2 milsover 20 gauge steel panels. Usually for elastomeric coatings, Swardhardness of about 10 or greater is desirable. For universal coatings,Sward hardness of about 14 or greater, and typically about 20 or greaterand preferably about 30 or greater is desirable. Usually for universalcoatings, flexibility at standard or lower temperatures as describedhereinabove is desirable.

Appearance is measured in terms of distinctness of image (DOI) which ismeasured by on Dori-Gon Meter D47-6 manufactured by Hunter Laboratories.Additionally, the coatings of this invention given an impression ofhaving a "wet-look" of a freshly applied and unbaked coating.

DETAILED DESCRIPTION OF THE INVENTION

The coating compositions of this invention are of high solids.Sprayability of these coating compositions can be about 40 percent orhigher and typically about 40 to 65 percent solids. To obtain the resinsand coating compositions of this invention, the starting materials areselected on the basis described more fully hereinbelow.

The starting hydroxy-functional polyepoxides useful herein are lowmolecular weight polyepoxides which can have 2 or more epoxy groups permolecule, and typically have more than 2 epoxy groups per molecule andpreferably 3 or more epoxy groups per molecule. The polyepoxides usefulhere can have epoxide equivalent weights of 50 to 1000 and preferably100 to 500, and hydroxy equivalent weights of 100 to 2000 and preferably300 to 600. Typical examples, thereof, include hydroxy-functional epoxyethers and esters which are preferred herein and others such as epoxygroup containing acrylic polymers which also contain a hydroxyl group;or a mixture thereof.

Illustrative examples of the epoxy ethers can be glycidyl ethers such asglycerol polyglycidyl ether (having about 3 epoxy groups);trimethylolpropane polyglycidyl either (having about 3 epoxy groups);diglycerol polyglycidyl ether (having about 3 epoxy groups); sorbitolpolyglycidyl ether (having about 4 epoxy groups); such as is availablefrom Nagase America Corporation under the Tradename "DENACOL".

Yet other hydroxy-functional epoxy resins can be prepared by modifyingan epoxy-containing material to produce a polyepoxide containing ahydroxy group and residual epoxy groups. For example, one or more epoxygroups of a polyepoxide can be reacted with organic acid or the like togenerate hydroxyl groups while retaining residual epoxy groups. As yetanother example, the hydroxyfunctional polyepoxides can be prepared byreacting one or more epoxy groups of a polyepoxide with, say, organicacid to generate hydroxyl groups, said hydroxyl groups may be reactedwith, say anhydrides to generate acid groups which may in turn furtherreact with epoxy groups of a polyepoxide. This process can yieldmolecules with high epoxy functionality, which molecules also containhydroxyl groups. Illustrative examples of polyepoxides which may bemodified include the triglycidyl isocyanate available from Ciba Giegy asARALDITE PT 810, butanediol diglycidyl ether, and3,4-epoxycylohexylmethyl-3,4- epoxycyclohexyl carboxylate.

Illustrative examples of the epoxy-functional acrylic polymers whichalso contain a hydroxyl group are copolymers of an ethylenicallyunsaturated monomer containing an epoxy group and an ethylenicallyunsaturated monomer containing a hydroxyl group. The copolymers areprepared by free radical polymerization of the ethylenically unsaturatedmonomers. Examples of the ethylenically unsaturated monomers containingan epoxy group can be a glycidyl acrylate, a glycidyl methacrylate, andan allyl glycidyl ether. Examples of ethylenically unsaturated monomerscontaining a hydroxyl group can be hydroxyethyl acrylate, hydroxypropylacrylate and the like. Other copolymerizable monomers different from theabove can be alkyl esters of acrylic or methacrylic acid, e.g., ethylacrylate, butyl acrylate or 2-ethylhexyl acrylate, ethyl methacrylate,butyl methacrylate and the like; vinyl monomers such as styrene, vinyltoluene and the like.

In preparing the epoxy-functional polyurethanes, isocyanates are reactedwith the hydroxyl groups of the aforedescribed polyepoxides. Theisocyanates including isocyanate prepolymers useful herein are of lowmolecular weight and have an isocyanate equivalent weight of 87 to 2000and preferably 87 to 1500. Examples of the useful isocyanates can bealiphatic or aromatic isocyanates. Illustrative examples of the usefulisocyanates can be simple isocyanates such as, isophorone diisocyanate,trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate,toluene diisocyanate; isocyanurates such as the isocyanurate availablefrom Mobay Chemical as "Des N-3390"; isocyanurate derived fromisophorone diisocyanate, commercially available from VEBA Company asT1890; biurets such as the biuret from 1,6-hexamethylene diisocyanate,commercially available from Mobay Chemical as DESMODUR N. The isocyanateprepolymers can be prepared by, say, reacting a polyisocyanate, inexcess, with an active hydrogen-containing material such as a polyol.

In preparing the epoxy-functional polyurethane, the isocyanate and thehydroxy-functional polyepoxide can be reacted in an equivalent ratio ofone isocyanate group to one or more hydroxyl group(s). The temperatureof the reaction can be from about 70° C. to 110° C. Catalysts such asdibutyltin dilaurate can be employed. Also, inert solvents can beemployed. The resultant product comprising the epoxy-functionalpolyurethane can have an epoxy equivalent weight of 200 to 1000 andpreferably 200 to 800.

Curing agents that are useful herein are of low molecular weight. Thecuring agents can be selected from the group consisting of polyacids,anhydrides, polyamines and a mixture thereof. Other curing agents suchas aminoplasts, isocyanates, blocked isocyanates, alkoxysilanes or thelike can be used, in complimentary amounts.

The polyacids typically have molecular weight from about 90 to 2000 andpreferably from about 300 to 1000. The polyacids can be simple polyacidsor their adducts. Usually, liquid polyacids are employed. Non-limitingexamples of these acids are succinic acid, glutaric acid, adipic acid,azelaic acid, oxalic acid, phthalic acid, isophthalic acid,hexahydrophthalic acid, methylhexahydrophthalic acid, maleic acid,chlorendic acid and the like. Also there can be employed polyacids ofhigher acid functionality, e.g., trimellitic acid, tricarballylic acid,aconitic acid and the like.

Non-limiting examples of the polyacid adducts can be acid-functionalpolyesters, acid-functional polyurethanes and the like. An example ofthe acid functional polyesters can be prepared by reacting excess of asimple polyacid as described above with a polyol. Alternately a polyacidanhydride such as described below can be reacted with the polyol, suchas 1,6-hexanediol, trimethylol propane and polycaprolactone triol or amixture thereof.

The anhydrides useful herein as curing agents comprise monoanhydrides oflow molecular weight. Examples of the monoanhydrides are alkylhexahydrophthalic anhydride wherein the alkyl group has up to 7 carbonatoms, e.g., methylhexahydropathalic anhydride. Other anhydrides thatcan be used herein include aliphatic, including cycloaliphatic, olefinicand cycloolefinic anhydrides and aromatic anhydrides. Substitutedaliphatic and aromatic anhydrides are also included within thedefinition of aliphatic and aromatic provided the substituents do notadversely affect the reactivity of the anhydride or the properties ofthe resultant product. Examples of substituents would be chloro, alkyland alkoxy. Examples of anhydrides include succinic anhydride,methylsuccinic anhydride, dodecenylsuccinic anhydride,octadecenylsuccinic anhydride, phthalic anhydride, tetrahydrophthalicanhydride, methyltetrahydrophthalic anhydride, hexahydrophthalicanhydride, alkylhexahydrophthalic anhydrides such asmethylhexahydrophthalic anhydride, tetrachlorophthalic anhydride,endomethylene tetrahydrophthalic anhydride, chlorendic anhydride,itaconic anhydride, citraconic anhydride and maleic anhydride.

In the practice of this invention as a coating composition, theepoxy-functional polyurethane and the curing agent can be employed in anamount sufficient to provide an effective cure wherein the cured coatingis hard and solvent-resistant. For example, the epoxy-functionalpolyurethane and a polyacid curing agent can be employed in an amount ofabout 0.8:1 to 1.2:1 based on the acid group to the epoxy group.

The particular epoxy-functional polyurethane and curing agent that areemployed will depend on the nature thereof and the desired properties ofthe resultant coating. In essence, the epoxy-functional polyurethane andthe curing agent, are selected on basis that will ensure the desiredhardness and/or flexibility of the cured coating. Generally put, forelastomeric coating, soft block epoxy-functional polyurethanes andcuring agents can be employed. For universal coatings, relatively harderblock ingredients can be employed. Also, combinations of hard block andsoft block epoxy-functional polyurethanes and the curing agents can beemployed in order to obtain the required hardness and/or flexibility.

Illustratively, for an elastomeric coating, an epoxy-functionalpolyurethane can be prepared by reacting a hydroxy functionalpolyepoxide available from Nagase America Corporation as DENACOL 421with an isocyanurate T 1890 commercially available from VEBA Company.The curing agent can be a polyacid adduct which is prepared by reactingmethyl hexahydrophthalic anhydride, with the trifunctionalpolycaprolactone polyol PCP 0305 available from Union CarbideCorporation. For a universal coating, the epoxy-functional polyurethanecan be prepared by reacting DENACOL 421 with an isocyanate prepolymerwhich is prepared by reacting excess isophorone diisocyanate, with apolyester polyol derived from hexahydropthalic anhydride, adipic acidand neopentyl glycol. The curing agent can be a polyacid derived fromtrimethylol propane and methyl hexahydropthalic anhydride.

It is envisaged that the coating compositions of this invention would bepracticed as multi pack, e.g., two-pack coating compositions. Forexample, the epoxy-functional polyurethane can be contained in one packand the curing agent and cure catalyst in another.

Typically, coating additives, such as ultraviolet light absorbers and/orstabilizers, flow control agents, antioxidants, plasticizers, and thelike can be added to the coating composition. These additives can beused in amounts up to about 25 percent by weight based on the totalresin weight.

The coating composition can be applied to the substrate by any of theconventional coating techniques such as brushing, spraying, dipping orflowing, but it is preferred that spray such as compressed air spraying,electrostatic spraying and either manual or automatic methods which arepreferred.

It is a distinct feature of the invention that the high solidsthermosetting coating compositions of this invention display anacceptably good sag control at a film thickness of up to about 2 mils.Considering that coating compositions comprising low molecular weightcomponents generally have sag control problems, it is indeed surprisingthat the instant coatings having low molecular weight components havethe acceptable sag control. Thus, relatively lower amounts, if any atall, of sag control agents need to be added to the coating composition.Therefore, these coating compositions do not suffer a reduced solidscontent and poorer appearance, as is otherwise the case with art-relatedhigh solids compositions wherein sag control agents are added.

After application of the coating composition to the substrate, thecoated substrate is heated to cure the coating. In the curing operation,solvents are driven off and the film-forming material is crosslinked.The heating or curing operation is usually carried out at a temperaturein the range of from 160°-350° F. (71°-177° C.) but if needed lower orhigher temperatures may be used depending upon whether it is sufficientto activate any necessary crosslinking mechanisms. The thickness of thecoating is usually from about 1 to 5, preferably 1.2 to 3 mils.

Preferably, the compositions of the present invention, particularlythose prepared with the aliphatic and cycloaliphatic polyepoxides areused to formulate clear coats for use in a color-plus-clear application.In a color-plus-clear application, a composite coating is applied to asubstrate. The process comprises applying to the substrate a pigmentedor colored film-forming composition to form a base coat and applying tothe base coat a second non-pigmented film-forming composition to form atransparent top coat over the base coat.

The film-forming composition of the base coat can be any of thecompositions useful in coating applications, particularly automotiveapplications in which the color-plus-clear coating applications arefinding frequent use. A film-forming composition conventionallycomprises a resinous binder and a pigment to act as a colorant.Particularly useful resinous binders are acrylic polymers, polyestersincluding alkyds and polyurethanes. The resinous binder for the basecoat can be an organic solvent-based material such as those described inU.S. Pat. No. 4,220,679, note column 2, line 24, continuing throughcolumn 4, line 40. Also, water-based coating compositions such as thosedescribed in U.S. Pat. No. 4,403,003 and U.S. Pat. No. 4,147,679 canalso be used as the binder in the base coat composition. The filmforming composition for the base coat can also be the epoxy-functionalpolyurethane and the curing agent of the present invention.

The base coat composition also contains pigments to give it color.Examples of suitable pigments for the base coat are described in theaforementioned U.S. Pat. Nos. 4,220,679, 4,403,003 and 4,147,679.

Optional ingredients in the base coat composition are those which arewell known in the art of formulating surface coatings and includesurfactants, flow control agents, thixotropic agents, fillers,anti-gassing agents, organic co-solvents, catalysts and other customaryauxiliaries. Examples of these materials and suitable amounts aredescribed in the aforementioned U.S. Pat. Nos. 4,220,679, 4,403,003 and4,147,679. The usual spray techniques and equipment for air spraying andelectrostatic spraying in either manual or automatic methods can beused.

During application of the base coat to the substrate, a film of the basecoat is formed on the substrate typically in a thickness of about 0.1 to5 and preferably about 0.1 to 2 mils. After forming a film of the basecoat on the substrate, solvent, that is, organic solvent and/or water,is driven out of the base coat film by heating or simply air drying fora period of time before application of the clear coat. Preferably, theheating step will only be that sufficient and for a short period of timeto insure that the clear top coat composition can be applied to the basecoat without the former dissolving the base coat composition, that is,"striking in". Suitable drying conditions will depend on the particularbase coat composition, on the ambient humidity with certain water-basedcompositions, but in general a drying time of from about 1 to 5 minutesat a temperature of about 68°-175° F. (20°-79° C.) will be adequate toinsure that mixing of the two coats is minimized. At the same time, thebase coat film is adequately wetted by the clear top coat composition sothat satisfactory intercoat adhesion can be obtained. Also, more thanone base coat and more than one top coat may be applied to developoptimum appearance. Usually between coats, the previously applied basecoat or top coat is flashed, that is, exposed to ambient conditions forabout 1 to 20 minutes.

The clear top coat composition is applied to the base coat by any of theconventional coating techniques mentioned above, although sprayapplications are preferred. As mentioned above, the clear top coat isapplied to the base coat via a wet-on-wet technique before the base coathas been cured. The two coatings are then heated to conjointly hardenboth coating layers. Curing conditions such as described above can beused.

The invention will be further defined by reference to the followingexamples. Unless otherwise indicated, all parts are by weight.

EXAMPLE 1

This example illustrates the epoxy-functional polyurethanes of thisinvention and methods of preparing the same. This entails firstpreparing a polyester polyol, followed by preparing an isocyanateprepolymer therewith, and reacting the prepolymer with ahydroxy-functional epoxy.

The polyester polyol was prepared as follows:

    ______________________________________                                        Ingredients       Parts by Weight (grams)                                     ______________________________________                                        Hexahydrophthalic anhydride                                                                     1488.9                                                      Triphenylphosphite                                                                              1.75            Charge A                                    Butylsulfonic acid                                                                              1.75                                                        Neopentyl glycol  2011                                                        ______________________________________                                    

Charge A in a properly equipped reaction vessel under a nitrogen blanketwas heated to 80° C. and neopentyl glycol was added. The reactionmixture was heated to 200° C. and held thereat for about 8 hours untilan acid value of about 10 was attained. The resultant composition wasthinned to 90% solids with methy amyl ketone.

The resultant composition comprising a polyester polyol was furtheresterified to form yet another polyester polyol as follows:

    ______________________________________                                        Ingredients        Parts by Weight (grams)                                    ______________________________________                                        The above polyester polyol at                                                                    2587                                                       90% solids in methyl amyl ketone                                                                 413                                                        Adipic acid                                                                   ______________________________________                                    

The above polyester polyol and adipic acid were charged to a properlyequipped reaction vessel and heated in a nitrogen atmosphere to react.Heating was continued to 200° C. and held thereat over a period of 5hours with removal of the methyl amyl ketone solvent and subsequentlywater from the esterification until an acid value of about 10 wasattained. The resultant product was thinned to about 90 percent solidswith butyl acetate and analyzed as follows. Solids content measured at110° C. for one hour was 83.0, viscosity was 24.3 stokes, acid value was8.5 and hydroxyl value was 150.5.

An isocyanate prepolymer was prepared with the above polyester polyol;the resultant prepolymer was reacted with a hydroxyl-functional epoxy.The following were used in the preparation.

    ______________________________________                                        Ingredients          Parts by Weight (grams)                                  ______________________________________                                        The polyester polyol from above                                                                    531.9                                                    Trimethylhexamethylene diisocyanate                                                                241.1                                                    Dibutyltin dilaurate 0.08                                                     Butyl acetate        26.8                                                     DENACOL 421.sup.1    492.7                                                    Butyl acetate        243.2                                                    ______________________________________                                         .sup.1 Diglycerol polyglycidyl ether available from Nagase America Co.   

To a properly equipped reaction vessel were charged the polyesterpolyol, the trimethylhexamethylene diisocyanate, the dibutyltindilaurate and butyl acetate and heated to 60° C. to react in a nitrogenatmosphere. There resulted an exotherm with the reaction temperaturerising to 101° C. The reaction mixture was cooled to 90° C. and heldthereat for about 2 hours and 15 minutes until a constant isocyanateequivalent weight of 980 was attained.

To the resultant mixture comprising the isocyanate prepolymer, DENACOL421 was added, heated to 90° C. and held thereat until all theisocyanate had reacted. Thereafter, butyl acetate was added to thereaction mixture to thin it to about 80 percent solids.

EXAMPLE 2

This example further illustrates the epoxy-functional polyurethanes ofthis invention and a method of preparing the same. The following wereused in the preparation.

    ______________________________________                                        Ingredients      Parts by Weight (grams)                                      ______________________________________                                        TERACOL 1000.sup.1                                                                             2599.9                                                       Isophorone diisocyanate                                                                        1154.3          Charge A                                     Dibutyltin dilaurate                                                                           0.4                                                          DENACOL 421      1648            Charge B                                     Butyl acetate    3585            Charge C                                     ______________________________________                                         .sup.1 A polyether polyol of molecular weight of about 1000, available        from E. I. du Pont de Nemours and Co.                                    

Charge A in a properly equipped reaction vessel was heated in a nitrogenatmosphere. The reaction mixture was held at 90° C. for about 4 hoursuntil a constant isocyanate equivalent weight of about 937 was attained.Charges B and C were added to the reaction vessel. The resulting mixturewas held at 90° C. until all the isocyanate had reacted. The reactionproduct was analyzed as follows. Solids content at 110° C. for one hourwas 61.0, viscosity was 44.2 stokes, epoxy equivalent was 857.

EXAMPLE 3

A high solids coating composition comprising the epoxy-functionalurethanes of this invention was prepared and used as follows:

    ______________________________________                                                           Parts by Weight                                                                           Resin                                          Ingredients        (grams)     Solids                                         ______________________________________                                        Package A                                                                     Epoxy-functional urethane.sup.1                                                                  19.9        12                                             Epoxy-functional urethane.sup.2                                                                  72          57.5                                           RESIMINE.sup.3 717 23.8        20.0                                           Oxyhexyl acetate   45                                                         Xylene             22.5                                                       Methyl amyl ketone 22.4                                                       Package B                                                                     TINUVIN 328.sup.4  3.0         3.0                                            TINUVIN 292.sup.5  0.5         0.5                                            Flow control agent.sup.6                                                                         1.0         0.1                                            Flow control agent.sup.7                                                                         0.9         0.5                                            Curing agent.sup.8 35.4        24.8                                           Curing agent.sup.9 8.1         5.7                                            ARMEEN DM 12D.sup.10                                                                             2.0         2.0                                            Oxyhexyl Acetate   8.8                                                        Xylene             4.4                                                        Metyl amyl ketone  4.4                                                        ______________________________________                                         .sup.1 The epoxyfunctional urethane was prepared in essentially the same      manner as described in Example 2. It had an epoxy equivalent of 857, a        solids content (at 110° C. for 1 hour) of 61.0 and viscosity of        44.2 stokes.                                                                  .sup.2 The epoxyfunctional urethane was prepared in essentially the same      manner as described in Example 1. It had an epoxy equivalent of 479, a        solids content (at 110° C. for 1 hour) of 79.9 and viscosity of        61.0 stokes.                                                                  .sup.3 Aminoplast curing agent available from Monsanto Chemical Co.           .sup. 4 UV absorber available from Ciba Geigy.                                .sup.5 UV stabilizer available from Ciba Geigy.                               .sup.6 Silicone fluid available as DC 200 (at 10 centi stokes) from Dow       Corning Corporation.                                                          .sup.7 Polybutyl acrylate flow control agent.                                 .sup.8 Polyacid curing agent derived from reacting 1,6hexanediol and          methylhexahydrophthalic anhydride in a mole ratio of 1:2.                     .sup.9 Polyacid curing agent derived from reacting trimethylolpropane and     methylhexahydrophthalic anhydride in a mole ratio of 1:3.                     .sup.10 Tertiary amine catalyst available from Armak Co.                 

Packages A and B were prepared separately by mixing the aboveingredients in the order indicated above at low shear with goodagitation. The two packages were combined in a ratio by weight of 3 to 1of Package A to Package B. The final composition having a spray solidscontent of about 46 percent was spray applied to metallic andelastomeric substrates and cured by heating to 121° C. (250° F.) forabout 30 minutes.

The coated substrate having a film thickness of 1.8 mils was evaluatedfor flexibility and hardness with the following results: The coatedsubstrates exhibited Sward hardness of 40 and withstood a 1/2-inchmandrel test at room temperature without a substantial break. Thecoating also has a remarkable appearance. Distinctness of image (DOI)over metallic substrates was 100, and over elastomeric substrate was 95.

EXAMPLE 4

This example further illustrates the high solids coating composition andmethods of preparing and using the same.

    ______________________________________                                                           Parts by Weight                                                                           Resin                                          Ingredients        (grams)     Solids                                         ______________________________________                                        Package A                                                                     The epoxy-functional urethane                                                                    87.8        70.3                                           described hereinabove                                                         Oxyhexyl acetate   26.9                                                       Xylene             13.4                                                       Methyl amyl ketone 13.4                                                       Package B                                                                     TINUVIN 328        3           3                                              TINUVIN 292        0.5         0.5                                            DC 200             1.0         0.1                                            Flow control agent.sup.2                                                                         0.9         0.5                                            Curing agent.sup.3 42.3        29.8                                           ARMEEN DM 12D      2.0         2.0                                            Oxyhexyl Acetate   10.5                                                       Xylene             5.3                                                        Metyl amyl ketone  5.2                                                        ______________________________________                                         .sup.1 The epoxyfunctional urethane was essentially as described in           Example 1. It had an epoxy equivalent weight of 556, solids content at        110° C. was 80.3 and viscosity was 180 stokes.                         .sup.2 Polybutyl acrylate.                                                    .sup.3 Polyacid curing agent derived from reactions 1,6hexanediol and         methylhexanydrophtalic anhydride in a mole ratio of 1:2.                 

The coating composition was formulated in essentially the same manner asdescribed in Example 3. The resultant coating composition having a spraysolids content of 50 percent was spray applied and evaluated forflexibility and hardness. The coated substrates exhibited Sward Hardnessof 22 and withstood a 1/2-inch mandrel test at room temperature withouta substantial break. Distinctness of image over metal was 90.

EXAMPLE 5

This example illustrates epoxy-functional polyurethane of this inventionand a method of preparing the same.

    ______________________________________                                        Ingredients       Parts by Weight (grams)                                     ______________________________________                                         T-1890L.sup.1      733                                                                                       Charge A                                      DENACOL 421       1822                                                        Butyl acetate      364          Charge B                                      ______________________________________                                         .sup.1 isocyanurate derived from isophorone diisocyanate and commercially     available from VEBA Company.                                             

Charge B was added to Charge A and heated to 90° C. and held thereatuntil all the isocyanate had reacted.

The resultant mixture comprising an epoxy-functional urethane wasanalyzed with the following results: Solids at 110° C. was 79.6 percent,viscosity was 22.2 stokes, epoxy equivalent was 256.

EXAMPLE 6

A coating composition was prepared with the above epoxy-functionalurethane and other ingredients listed hereinbelow:

    ______________________________________                                                           Parts by Weight                                                                           Resin                                          Ingredients        (grams)     Solids                                         ______________________________________                                        TINUVIN 328        3.0         3.0                                            TINUVIN 292        0.5         0.5                                            DC 200             1.0         0.1                                            Flow control agent.sup.1                                                                         0.9         0.5                                            Solvent Blend.sup.2                                                                              50.2                                                       Epoxy-functional polyurethane                                                                    68.6        54.9                                           of Example 5                                                                  Curing agent.sup.3 54.2        36.3                                           Curing agent.sup.4 12.5        8.8                                            ARMEEN DM 12D      2.0         2.0                                            ______________________________________                                         .sup.1 The flow control agent was polybutyl acrylate.                         .sup.2 Comprising oxyhexyl acetate, xylene and methyl amyl ketone.            .sup.3 Polyacid curing agent derived from 1,6hexanediol and                   methylhexanydrophtalic anhydride in a mole ratio of 1:2.                      .sup.4 Polyacid curing agent available from reacting trimethylolpropane       and methylhexahydrophthalic anhydride in a mole ratio of 1:3.            

The coating composition was prepared by blending the above thoroughlyand the resultant coating composition at as 55 percent resin solids wasspray applied to metallic and elastomeric substrates, cured, andevaluated in essentially the same manner as described in Example 3.

The coated and cured substrates were found to have excellent appearance;distinctness of image over metallic substrates of 100, and distinctnessof image over elastomeric substrates of 70; excellent room temperatureflexibility, good flexibility at 20° F.; Sward hardness of 16, excellentsolvent resistance; and good impact resistance.

What is claimed is:
 1. A low molecular weight epoxy-functionalpolyurethane which is prepared by reacting:(a) an isocyanate with (b) ahydroxy-functional polyepoxide having more than 2 epoxy groups permolecule.
 2. A low molecular weight epoxy-functional polyurethane ofclaim 1, wherein the isocyanate equivalent weight is about 87 to 2000.3. An epoxy-functional polyurethane of claim 1, wherein the isocyanateis a simple polyisocyanate, a biuret, an isocyanurate, isocyanateprepolymer or a mixture thereof.
 4. An epoxy-functional polyurethane ofclaim 1, wherein the hydroxy-functional polyepoxide has an epoxyequivalent weight of about 50 to
 1000. 5. An epoxy-functionalpolyurethane of claim 1, wherein the hydroxy-functional polyepoxide hasa hydroxy equivalent weight of about 100 to
 2000. 6. An epoxy-functionalpolyurethane of claim 1, wherein the hydroxy-functional polyepoxide is ahydroxy-functional polyglycidyl either.
 7. A high solids theremosettingcoating composition comprising:(a) the epoxy-functional polyurethane ofclaim 1, and (b) a curing agent which is selected from the groupconsisting of polyacids, anhydride, polyamine and a mixture thereof. 8.A high solids theremosetting coating composition of claim 7, wherein thepolyacid is (a) derived from reacting 1,6-hexandiol andmethlhexahydrophthalic anhydride in a mole ration of 1:2 or the polyacidis (b) derived from reacting trimethylolpropane or polycaprolactonetriol or mixture thereof with methylhexahydropthalic anhydride in a moleratio of about 1:3, or (c) a mixture of (a) and (b).
 9. A high solidstheremosetting coating composition as recited in claim 7 which furthercomprises an aminoplast or an isocyanate, a blocked isocyanate oralkoxysilane as a curing agent.
 10. A high solids theremosetting coatingcomposition of claim 7, having a sprayability of 40 to 65 percent orhigher.